It is important to share the reasoning evidence between contractor (IT vendor) and contractee (customer) when entering into a software development project, to achieve satisfactory agreement in estimating development volume. However, IT vendors usually find it difficult to explain the detail of system complexity to customers who have little knowledge about software development. This tends to result in complaint and dissatisfaction for such estimating effort. In this paper, we have applied CoBRA(Cost estimation Benchmarking and Risk Assessment) method for evaluating system requirement, found that the system complexity and the performance requirement are closely related as the cause of estimation discrepancy between IT vendor and customer, and made it clear that the visual explanation for these two factors is a key for the success of software development.
